Chlorofluorocarbons (CFCs) like trichlorofluoromethane and dichlorodifluoromethane have been traditionally used as refrigerants, blowing agents and diluents for gaseous sterilization. In recent years, there has been universal concern that completely halogenated chlorofluorocarbons might be detrimental to the Earth's ozone layer. Therefore, stratospherically safer alternatives to these materials are desirable.
There is presently a worldwide effort to use fluorine-substituted hydrocarbons which contain fewer or no chlorine substituents. The production of HFCs, i.e. compounds containing only carbon, hydrogen and fluorine, has been the subject of interest to provide environmentally desirable products that could provide a substitute to CFCs. Such compounds are known in the art to be produced by reacting hydrogen fluoride with various hydrochlorocarbon compounds. While HFCs are considered to be much more environmentally advantageous than hydrochlorofluorocarbons (HCFCs) or chlorofluorocarbons (CFCs) because they are not non-ozone depleting, recent data indicates that they may also contribute to greenhouse global warming. Accordingly, alternatives to HFCs, HCFCs, and CFCs are also being explored.
Hydrofluoroolefins (“HFOs”) present one possibility as replacements because they exhibit low ozone depletion potential and contribute little to greenhouse global warming. One such HFO is 2,3,3,3-tetrafluoropropene (HFO-1234yf), which has been well characterized as effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid. It may be produced by a number of different methods including those described within U.S. Patent Application Nos. 20070197842, 20070112229, 20090124837, 20090287026, 20090240090, and 20090234165, the contents of which are incorporated herein by reference.
U.S. Patent Application No. 20090234165, in particular, discloses the formation of 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) as an intermediate in the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf). One drawback to this reaction, however, is that impurities present throughout the reaction process (e.g. catalysts, reaction by-products, process starting materials, and the like) interfere with the isolation and conversion of HFC-236ea. Halocarbon reactant or by-product impurities that are particularly problematic include, but not limited to, 1,1,1,2,3-pentafluoropropane, 1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoropropane, 1,1,1,3-tetrafluoropropane, (E)1,2,3,3,3-pentafluoropropene, (Z)1,2,3,3,3-pentafluoropropene, 3,3,3-trifluoropropene, 1,1,1-trifluoropropane, 3,3,3-trifluoropropyne, (Z)1,3,3,3-tetrafluoropropene, and (E)1,3,3,3-tetrafluoropropene. Accordingly, methods for isolation/purification of HFC-236ea from such compounds are desirable.
It is generally known that azeotrope and azeotrope-like compositions provide good mechanisms for product purification. Of particular interest are mixtures containing hydrofluorocarbons and hydrogen fluoride, which are useful in the preparation and/or purification of desirable hydrofluorocarbons and chlorofluorolefin products. The identification of such compositions is difficult, however, because of the relative unpredictability of azeotrope formation. Therefore, industry is continually seeking new HFO-based mixtures that are acceptable and/or may be used to produce HFOs or HFO-based mixtures that are environmentally safer substitutes for existing CFCs, HCFCs, and HFCs.
This invention satisfies these needs among others.